The present invention enables to reduce deterioration in an uplink capacity due to a transmission power of an E-DPCCH, by setting, at the radio network controller, a suitable transmission power offset depending on a situation. A transmission power control method according to the present invention includes: measuring, at the radio base station, a reception quality of the enhanced dedicated physical control channel; notifying, from the radio base station to a radio network controller, the measured reception quality of the enhanced dedicated physical control channel; setting, at the radio network controller, a transmission power offset for the enhanced dedicated physical control channel to a dedicated physical control channel, in accordance with the reception quality of the enhanced dedicated physical control channel; and notifying, from the radio network controller to the mobile station, the set transmission power offset.